Process of treating cellulose



April 1934- G. SCHNEIDER PROCESS OF TREATING CELLULOSE Original FiledJan. 4, 1929 INVENTOR George Schneider Y ATTORNEY Patented Apr. 24, 1934PA Er FFlCE PROCESS OF TREATING CELLULOSE George Schneider, Mcntclair,N. 5., assignor to Celanese Corporation of America, a corporation ofDelaware Original application January 4, 1929, Serial No. 330,245.Divided and this application July 15, 1931, Serial No. 550,931. InCanada December Claims.

This invention relates generally to an improved process of the treatmentof cellulose prior to the esteriiication of the same and particularly tothe treatment of cellulosic material prior to acetyla- 5 tion. 7

This application is a division of my application Serial No. 330,245filed January 4, 1929.

An object of my invention is to provide a process for the pretreatmentof cellulose which will .10 not only facilitate its esterification butwill also yield superior products.

Another object of my invention is to devise'a process for thepretreatment of cellulosic material which will consume but a smallfraction of the time heretofore required for such operations.

Another object of my invention is to devise a process whereby the stepsof pretreating the cellulosic material and esterifying the same can becombined into a single and continuous operas tion.

Another object of my invention is to employ an apparatus for thepretreating of cellulosic material which is compact and efficient. Otherobjects and advantages will appear from the following detaileddescription.

The pretreatment of cellulosic material to facilitate the esterificationthereof has been proposed heretofore and has'been used to some extentwith varying degrees of success. The processes employed have been rathercumbersome and involve the use of unwieldy and uneconomical apparatus.These processes were conducted as separate and distinct operations fromthat of acetylation and involved a large amount of efiort and requiredconsiderable time.

Generally heretofore, the pretreatment of cellulosic material has beeneffected in a rotary apparatus constructed to give thorough tumblingand/or mixing or in a stationary apparatus provided with agitatingmeans. These types of apparatus were objectionable for various reasons.

The rotating apparatus in order to insure thorough tumbling and mixingofthe cellulose must be of such size that its volume is about threetimes that of the cotton or cellulose being treated. In order for suchan apparatus to take an amount of cellulose as is actually employed asan acetylizing charge, its size would be so large that it would precludethe installation of such an apparatus with each acetylizer. Anotherdisadvantagearising from the use of such rotating apparatus is the factthat the discharge of the pretreated material from the apparatus when 55placed over the acetylizer is mechanical but not uniformly constant.This gives a nonuniformly acetylized product.

The stationary type of apparatus heretofore employed has also been foundobjectionable. Its use necessitated the removal of the pretreated 68material therefrom by hand and also the subse- -'quent charging of theacetylizer by hand.

Naturally these operations are slow and greatly curtail the productivityof an acetylizing unit. Not only is this method and apparatusinefiicient but it is also hazardous to the health of the employeessince it entails disagreeable exposure to the strong acetic acid vaporsand fumes. I

To overcome these disadvantages and draw- 7c backs I have invented thepresent apparatus and process. My apparatus is of simple constructionand consists of a pretreater which ispreferably rectangular in shapeandprovided with agitators. This rectangular container is arranged incombination with an acetylizer so that the contents of the former aredischarged directly into the latter. The container is also provided withmeans for introducing the pretreated liquid and also with an opening forcharging the cotton or other cellulosic material thereinto and adischarge means into the acetylizer.

The pretreatment process comprises the. treatmentof the cellulosicmaterial with a relatively small proportion of a lower fatty acid suchas formic acid or acetic acid or with a mineral acid such ashydrochloric acid. a The formic or acetic acid may be applied to thecellulosic material in any suitable manner, either in the form of aliquid, or in the form of a vapor. One mode of pretreatment comprisesthe agitation of the cellulosic material with a relatively small amountof glacial acetic acid in a suitable apparatus, say a horizontal type ofagitator. Instead of glacial acetic acid, weaker acetic acid of from50%. to strength may be used.

The temperature of the pretreatment may be boiling temperatures of theorganic acid used, or it may be below such temperature, and may beordinary temperature or even below ordinary r temperature. The time oftreatment may be varied from one hour to five hours or more, dependingon the concentration, amount and nature of the organic acid used, andthe temperature employed. The amount of the lower fatty acid used may bevaried within wide limits, but we have found that if glacial acetic acidis used, excellent results are obtained by employing 10 to 30 parts ofthe glacial acetic acid to parts of the cellulose.

Because of the greater speed of reaction, the output of a givenesterifying apparatus is increased from 50 to 60%. Moreover, since bythis process, the amount of cooling required is less than in the formerprocesses, a great saving is effected. Moreover, by my process, it isnot necessary to precool the esterifying mixture in a separate vessel asis now the common practice, so that the expensive precoolers now usedmay be eliminated by the substitution of mere measuring devices whichare much cheaper.

The process may be employed for preparing various organic esters ofcellulose such as cellulose acetate, cellulose formate, cellulosepropionate or cellulose butyrate. Fowever, further details will be givenwith respect to the manufacture of cellulose acetate and the propertiesof cellulose acetate produced in accordance with my invention.

Cellulose acetate prepared from cellulosic material pretreated inaccordance with this invention has a clarity of about 20 whereascellulose acetate prepared from cellulosic material under identicalconditions but without pretreatment has a clarity of only 12. (The unitsgiven as a measure of the clarity are determined by dissolving 6 gramsof cellulose acetate in ice parts of acetone and are expressed in termsof centimeters of depth of the solution, which, when placed in the tubeis so opaque as to just prevent a black spot at the bottom of the tubeto be discernible when illuminated by a bright light.)

In the accompanying drawing The figure illustrates, diagrammatically oneembodiment of my apparatus. In the drawing a pretreater is representedat 1, the pretreater being preferably rectangular in shape and providedwith a hinged door 2 through which the material to be treated ischarged. To agitate the cellulosic material being treated, I provide astirrer comprising a horizontal shaft 3 provided along its length with aplurality of arms 5, the arms 5 being supplied or formed at their outerends with blades 4. These blades 4 are arranged in such a manner and atsuch angles that the rotation of the shaft 3 will cause the blades todeliver the cellulosic material to the opening 6 of the pretreater.

The opening 6 at the bottom of the pretreater is adapted to be closed bythe door 7 hinged as at 8. Attached to the pretreater so as to receivethe material delivered through the opening 6 is a chute 9. This chute ispreferably constructed in two sections, the lower portion 10 beinghinged as at 11 to enable its being swung into and out of alignment withthe upper rigid portion 9. The chute 9 is arranged to deliver thepretreated cellulosic material into the acetylizer or reaction chamber12. The acetylizer 12 is provided with any suitable stirrers or agitator14 mounted on shafts 15. The acetylizer is supported on the standards 16and is adapted to be tipped or tilted about the pivot 13 for dischargingits contents. Suitable covers for the acetylizer are also provided, butfor the sake of simplicity these have not been shown in the drawing.Obviously the hinged doors 2 and 7 can be replaced by sliding doors ifdesired. Also a cloth or other flexible tube or means may be substitutedfor the chute 9 for delivering the pretreated material to theacetylizer.

To introduce the pretreating liquid into the pretreater, I provide a potor kettle 17 which has a discharge pipe 19 terminating, within thepretreater, in a plurality of outlets 20. The supply of liquid to thispipe 19 and the outlets 20 is regulated by the valve 18. The shaft 3 isrotated by means of the belt and pulley 21 which is connected with anysuitable source of power, the shaft 3 being provided with suitablebearings 22.

The operation of the apparatus is as follows: The desired charge ofcellulosic material is introduced into the pretreater through 2 and theshaft 3 rotated, the door '7 being in the closed position. Thepretreating liquid, (acetic acid, formic acid, acetic and nitric acids,or other pretreating liquid) is put into the pot 17 and introduced intothe pretreater at a suitable rate by opening the valve 18. Due to thecomparatively large volume of the pretreater and the constant agitation,the liquid introduced is vaporized and uniformly distributed throughoutthe cellulosic material. After the desired degree of activity of thecellulose has been attained the chute 10 is put into operative positionand the door 7 opened. The rotation of the shaft 3 delivers thecellulosic materials to the opening 6 and the material discharges intothe acetylizer 12 at a regular rate which can be governed by the speedof rotation of the shaft 3. Before the pretreatment of the cellulosicmaterial is completed, the acetylizing mixture is introduced into theacetylizer and cooled to the desired temperature, for example to 0 to 2C. The pretreated cellulose is then introduced into the acetylizer 12.

After all of the cellulose has been delivered to 12, the chute 10 israised to the non-operative position as shown in dotted lines on thedrawing, the door 7 closed and a new charge of cellulosic materialintroduced into the pretreater for pretreatment. The cellulosic materialand acetylizing mixture are thoroughly agitated and mixed until thedesired amount of acetyl groups have been introduced into the cellulosemolecule when the reaction mixture is removed from the acetylizer bytilting the latter at 13. The reaction mixture is then subjected to theusual ripening, secondary and purification treatments.

The pretreater 3 may be constructed of acid resistant metal or of woodor both, as is deemed most economical under existing conditions andaccording to the pretreating agent used. The shaft 3 and the stirrerarms and blades are preferably made of acid resistant metal. The blades4 may be replaced by a continuous helical ribbon stirrer but I havefound that the use of fingers for segments of such a helical ribbon intheir outer ends, as shown in the drawing, is preferable. The acetylizershould preferably be surrounded by a hollow jacket through which a fluidheating or cooling medium can be passed to control the temperature ofthe reaction mixture. Instead of the tilting type of acetylizer shown, Imay employ an acetylizer provided in its bottom with a valve fordischarging the reaction mixture or other type of reactor.

Example The cellulosic material is charged into the pretreater throughthe top door 2 and the pretreating liquid, in this case, glacial aceticacid in amount of 20 lbs. per 100 lbs. of cotton is sprayed on itthrough the nozzles 20.

While the pretreatment is going on, the acetylizer 12 is charged with500 to 600 lbs. of a mixture of acetic acid and acetic anhydride, theacetic anhydride comprising 37 to 39% of the mixture. This mixture ofacetic anhydride and acetic acid also contains about 2 oz. of H2SO4. Themixture is then-cooled to about 0 to 5 C.

After the cellulosic material has been pretreated for a period of about3 hours the bottom discharge door '7 is opened and the pretreatedmaterial is fed through the chute 12 into the prepared cooled acidmixture in the acetylizer, 12.

The temperature of the reaction mixture rises to about 12 to 15 C. Whenthe latter point is reached 2 ounces of sodium carbonate are added tothe mass, with continued stirring for about 1 hour. The temperature isreduced to about 5 to 8 C. and a mixture containing 13 to 16 lbs. ofsulfuric acid and 100 lbs. of a mixture of glacial acetic acid andacetic anhydride of the strength above mentioned is added. ihetemperature rises to about 43 C. in about half an hour, and theacetylation is now virtually complete. The mass is new cooled andripened in any desired manner to normal acetone or any other desiredsolubility.

The pretreatment of the cellulosic material in the manner aboveindicated yields a final esterified product superior to that obtainedfrom the esterification of untreated cellulosic material. It has ahigher clarity and is more stable than the product obtained fromuntreated cellulosic material and in addition possesses more desirableviscosity characteristics. A further advantage, perhaps the mostimportant, is the fact that a pretreating operation as above set outshortens considerably the time required for esterification.

Having described my invention what I claim and desire to secure byLetters Patent is:

1. Process for the production of uniformly esterified cellulose whichcomprises pretreating cellulose in a fixed pretreatment chamber byintroducing a lower fatty acid into said chamber at a regular rate,agitating the cellulose within the chamber and then graduallydischarging the pretreated cellulose directly into an esterificationmixture.

2. Process for the production of uniformly acetylated cellulose whichcomprises pretreating cellulose in a fixed pretreatment chamber byintroducing acetic acid into said chamber at a regular rate, agitatingthe cellulose within the chamber and then gradually discharging thepretreated cellulose directly into an acetylating mixture.

3. Process for the production of uniformly esterified cellulose whichcomprises pretreating cellulose in a fixed pretreatment chamber byintroducing a lower fatty acid into said chamber at a regular rate,agitating the cellulose by lifting the same and allowing it to fallwithin the chamber and then discharging the pretreated cellulose at auniform rate directly into an esterification mixture.

4. Process for the production of uniformly acetylated cellulose whichcomprises pretreating cellulose in a fixed pretreatment chamber byintroducing acetic acid into said chamber at a regular rate, agitatingthe cellulose by lifting the same and allowing it to fall within thechamber and then discharging the pretreated cellulose at a uniform ratedirectly into an acetylating mixture.

5. Process for the production of uniformly acetylated cellulose whichcomprises pretreating cellulose in a fixed pretreatment chamber byintroducing acetic acid into said chamber at a regular rate, agitatingthe cellulose by lifting the same and allowing it to fall within thechamber and then discharging the pretreated cellulose at a uniform ratedirectly into an acetylating vessel containing 875 parts of anacetylating mixture comprising about 15 lbs. of sulphuric acid, 37 to39% of acetic anhydride and the balance glacial

